Atmosphere around small bodies
Bodies with small gravity might be hard to terraform. In this section, we discuss only about the Atmosphere, not about other features. Challenges If gravity is too low, an atmosphere will tend to escape. Already some small bodies in Solar System are experiencing this. Pluto and Triton are losing gasses. Small bodies usually lack of magnetic fields. If somehow they were terraformed, it is better to be within the magnetic shield of a larger body (like the moons of Saturn or Jupiter). They will have a very large atmosphere. This material shows that a breathable atmosphere around Pluto will be wider then the planet's radius. So, it will have more gas then Earth's atmosphere, creating a big greenhouse effect. This is because, without enough gravity, weight of outer gas layers is smaller, so they don't develop enough pressure to compress inner layers. A wide atmosphere will be in higher risk of getting lost. Huge amounts of gas will be needed to compensate the loss. However, in case of a larger body, like Luna or Jovian moons, the loss will be not that much. In the need of keeping an Atmosphere down, heavy inert gases could be used. In case of Saturnian moons, there is another challenge. Assuming a terraformed Enceladus or Mimas, the strong gravity of Saturn might pull away some of the atmosphere. There are a few high-tech methods to help these tiny worlds become new homes: *Paraterraforming - covering them with a transparent shield *Let them covered with water and cover the water with a transparent floating shield (also to create greenhouse effect) *Continuously feeding the atmosphere with new gasses *Artificial gravity (maybe in the far future). Calculation At Atmosphere Parameters, there are a few formulas, that allow us to have an image if the atmosphere can survive and for how long. Stability number is an approximation of how would certain gasses remain in an atmosphere. If the number is below 10, that gas will not escape into space. If the number is between 10 and 100, it will be lost, but in more then 1000 years. However, if the number is above 100, the specified gas will escape into space fast and differences can be seen during a human lifetime. Atmosphere height is an approximation of how high will the atmosphere rise, both at a breathable pressure and as an overall. The mathematical formula does not count that if the atmosphere is very large (for example, over a planetary radius), there, gravity will be very weak and in fact the gasses will extend further. If, by calculation, we conclude that the atmosphere will expend to a planetary diameter, then we can conclude that it is unstable even for short periods of time. Solar wind erosion works on all celestial bodies not protected by a magnetosphere. There is no accurate formula for that. On shorter timescales, like a human life, it is negligible. Ionizing radiation breaks apart water molecules, releasing hydrogen which escapes into space. This is important if water vapors reach too high altitudes. Candidates The following is a list of celestial bodies in the Solar System. For each of them, atmospheric parameters are included. Plain values indicate safeness. Italic values indicate something that is safe for a limited time (a few thousand years), while bold values are not safe. Inner planets Mercury - see Mercury Simulation *Oxygen stability (15 degrees C): 10.86 *Oxygen stability (400 degrees C): 25.37 *Water stability (15 degrees C): 19.30 *Water stability (400 degrees C): 45.09 *Hydrogen stability (15 degrees C): 173.7 *Hydrogen stability (400 degrees C): 405.8 *Atmosphere breathable height: 36.4 km *Atmosphere total height: 126 km Venus - see Venus Simulation *Oxygen stability (15 degrees C): 4.44 *Oxygen stability (50 degrees C): 4.98 *Water stability (15 degrees C): 7.90 *Water stability (50 degrees C): 8.86 *Hydrogen stability (15 degrees C): 71.09 *Hydrogen stability (50 degrees C): 79.72 *Atmosphere breathable height: 9 km *Atmosphere total height: 32 km Earth - no simulation conducted, using the facts *Oxygen stability (15 degrees C): 4.116 *Water stability (15 degrees C): 7.320 *Hydrogen stability (15 degrees C): 65.88 *Atmosphere breathable height: 8.4 km *Atmosphere total height: 25 km Luna - see Luna Simulation *Oxygen stability (15 degrees C): 19.237 *Oxygen stability (100 degrees C): 24.91 *Water stability (15 degrees C): 34.20 *Water stability (400 degrees C): 44.29 *Hydrogen stability (15 degrees C): 307.8 *Hydrogen stability (400 degrees C): 398.5 *Atmosphere breathable height: 75.8 km *Atmosphere total height: 2546 km Mars - see Mars Simulation *Oxygen stability (15 degrees C): 6.933 *Oxygen stability (-50 degrees C): 5.370 *Water stability (15 degrees C): 12.33 *Water stability (-50 degrees C): 9.546 *Hydrogen stability (15 degrees C): 110.9 *Hydrogen stability (-50 degrees C): 85.91 *Atmosphere breathable height: 25 km *Atmosphere total height: 67 km. Ceres - see Ceres Simulation *Oxygen stability (15 degrees C): 91.56 *Oxygen stability (-50 degrees C): 70.9 *Water stability (15 degrees C): 162.8 *Water stability (-50 degrees C): 126 *Hydrogen stability (15 degrees C): 1465 *Hydrogen stability (-50 degrees C): 1134 *Atmosphere breathable height: 595 km *Atmosphere total height: 1771 km. Jupiter system Io - see Io Simulation *Oxygen stability (15 degrees C): 17.97 *Oxygen stability (-100 degrees C): 10.80 *Water stability (15 degrees C): 31.94 *Water stability (-100 degrees C): 19.19 *Hydrogen stability (15 degrees C): 247.5 *Hydrogen stability (-100 degrees C): 172.7 *Atmosphere breathable height: 63 km *Atmosphere total height: 165 km. Europa - see Europa Simulation *Oxygen stability (15 degrees C): 22.78 *Oxygen stability (-100 degrees C): 13.68 *Water stability (15 degrees C): 40.49 *Water stability (-100 degrees C): 24.33 *Hydrogen stability (15 degrees C): 364.4 *Hydrogen stability (-100 degrees C): 219.0 *Atmosphere breathable height: 76 km *Atmosphere total height: 250 km. Ganymede - see Ganymede Simulation *Oxygen stability (15 degrees C): 16.73 *Oxygen stability (-100 degrees C): 10.06 *Water stability (15 degrees C): 29.75 *Water stability (-100 degrees C): 17.88 *Hydrogen stability (15 degrees C): 160.9 *Hydrogen stability (-100 degrees C): 267.8 *Atmosphere breathable height: 47 km *Atmosphere total height: 143 km. Callisto - see Callisto Simulation *Oxygen stability (15 degrees C): 18.87 *Oxygen stability (-100 degrees C): 11.34 *Water stability (15 degrees C): 33.54 *Water stability (-100 degrees C): 20.16 *Hydrogen stability (15 degrees C): 301.9 *Hydrogen stability (-100 degrees C): 181.4 *Atmosphere breathable height: 55 km *Atmosphere total height: 160 km. Saturn system Titan - see Titan Simulation *Oxygen stability (15 degrees C): 17.44 *Oxygen stability (-150 degrees C): 7.45 *Water stability (15 degrees C): 31.01 *Water stability (-150 degrees C): 13.25 *Hydrogen stability (15 degrees C): 279.1 *Hydrogen stability (-150 degrees C): 119.3 *Atmosphere breathable height: 64 km *Atmosphere total height: 189 km. Iapetus - see Iapetus Simulation *Oxygen stability (15 degrees C): 78.1 *Oxygen stability (-150 degrees C): 33.37 *Water stability (15 degrees C): 138.8 *Water stability (-150 degrees C): 59.32 *Hydrogen stability (15 degrees C): 1249 *Hydrogen stability (-150 degrees C): 533.9 *Atmosphere breathable height: 330 km *Atmosphere total height: 1000 km. Dione - see Dione Simulation *Oxygen stability (15 degrees C): 90.22 *Oxygen stability (-150 degrees C): 38.56 *Water stability (15 degrees C): 160.4 *Water stability (-150 degrees C): 68.55 *Hydrogen stability (15 degrees C): 1443 *Hydrogen stability (-150 degrees C): 616.9 *Atmosphere breathable height: 416 km *Atmosphere total height: 1238 km. Rhea - see Rhea Simulation *Oxygen stability (15 degrees C): 64.14 *Oxygen stability (-150 degrees C): 27.41 *Water stability (15 degrees C): 128.3 *Water stability (-150 degrees C): 54.83 *Hydrogen stability (15 degrees C): 1154 *Hydrogen stability (-150 degrees C): 1034 *Atmosphere breathable height: 297 km *Atmosphere total height: 880 km. Tethys - see Tethys Simulation *Oxygen stability (15 degrees C): 117.1 *Oxygen stability (-150 degrees C): 65.88 *Water stability (15 degrees C): 208.1 *Water stability (-150 degrees C): 88.95 *Hydrogen stability (15 degrees C): 1873 *Hydrogen stability (-150 degrees C): 800.1 *Atmosphere breathable height: 470 km *Atmosphere total height: 1397 km. Uranus Oberon - see Oberon Simulation *Oxygen stability (15 degrees C): 63.34 *Oxygen stability (-175 degrees C): 21.58 *Water stability (15 degrees C): 112.6 *Water stability (-175 degrees C): 38.36 *Hydrogen stability (15 degrees C): 1013 *Hydrogen stability (-175 degrees C): 345.2 *Atmosphere breathable height: 260 km *Atmosphere total height: 750 km. Titania - see Titania Simulation *Oxygen stability (15 degrees C): 59.54 *Oxygen stability (-175 degrees C): 20.28 *Water stability (15 degrees C): 105.9 *Water stability (-175 degrees C): 36.06 *Hydrogen stability (15 degrees C): 952.8 *Hydrogen stability (-175 degrees C): 324.5 *Atmosphere breathable height: 245 km *Atmosphere total height: 710 km. Ariel - see Ariel Simulation *Oxygen stability (15 degrees C): 82.53 *Oxygen stability (-175 degrees C): 28.11 *Water stability (15 degrees C): 146.7 *Water stability (-175 degrees C): 49.98 *Hydrogen stability (15 degrees C): 1320 *Hydrogen stability (-175 degrees C): 908.0 *Atmosphere breathable height: 380 km *Atmosphere total height: 1100 km. Umbriel - see Umbriel Simulation *Oxygen stability (15 degrees C): 88.14 *Oxygen stability (-175 degrees C): 30.02 *Water stability (15 degrees C): 156.7 *Water stability (-175 degrees C): 53.38 *Hydrogen stability (15 degrees C): 1410 *Hydrogen stability (-175 degrees C): 480.4 *Atmosphere breathable height: 360 km *Atmosphere total height: 1070 km. Neptune & Beyond Triton - see Triton Simulation *Oxygen stability (15 degrees C): 33.70 *Oxygen stability (-200 degrees C): 8.55 *Water stability (15 degrees C): 59.91 *Water stability (-200 degrees C): 12.21 *Hydrogen stability (15 degrees C): 539 *Hydrogen stability (-200 degrees C): 137 *Atmosphere breathable height: 110 km *Atmosphere total height: 300 km. Pluto - see Pluto Simulation *Oxygen stability (15 degrees C): 47.98 *Oxygen stability (-215 degrees C): 9.683 *Water stability (15 degrees C): 85.30 *Water stability (-215 degrees C): 17.21 *Hydrogen stability (15 degrees C): 609 *Hydrogen stability (-215 degrees C): 123 *Atmosphere breathable height: 130 km *Atmosphere total height: 400 km. Others Other moons and asteroids, not listed here, are unable to sustain an atmosphere for long enough periods of time. For them, many (if not all) values appear bold, showing that the atmosphere is unstable even during a human lifetime. The only one included is Ceres, which is on the list for comparison. Beyond Neptune, there is not enough light for plants to survive. Terraforming will also require an artificial source of light, which will also bring in some heat. Because of this, all data will change. This is why, no celestial body beyond Neptune was included in the list, except for Pluto which is listed for comparison. Update After Pluto Encounter On July 14th 2015, New Horizons reached the distant Pluto. What the tiny spacecraft found, will make us re-consider many of our existing theories. Images and data from Pluto has left scientists puzzled. One of the most important findings, at least for future terraforming, is the strange looking of Pluto's atmosphere. As the image shows, Pluto has a gigantic atmosphere, stretching as far as its outer moons. And all this atmosphere is not enough to compress the lower layers up to a pressure that humans will support. Pluto has the big advantage of a very low solar wind. If the solar wind was as strong as it is around Earth, for sure there would be almost no atmosphere. This comes with a very hard question: Can such a small celestial body be terraformed? Is it possible to compress or to replenish all that gas? Adding extra gas into Pluto's atmosphere will not be a hard job. After all, the Plutonian crust is full with frozen gasses. Just make some greenhouse effect and all will start to sublimate or boil. Bringing extra gasses from other Kuiper Belt Objects might also be possible. However, keeping them fixed, will be very hard. Pluto's atmosphere has a very low pressure: 0.2 to 0.3 Pa (1/400 000 of Earth's). And even at this very low surface pressure, the escape rate is alarming: 500 tons per hour! Guess that if the atmosphere were to have the same density as Earth's, the escape rate will be 55 000 tons per second. At that huge escape rate, you will need to crash 4 of Rosetta's 67P/Churyumov–Gerasimenko comets every Earth year, to replenish the gas losses. Heating all that material, so far away from the Sun, will require an artificial source of heat. As the new gasses boil into the atmosphere, they create an anti-greenhouse effect. and also, we must not forget that gasses ejected from a comet are not breathable: carbon monoxide and dioxide, methane, ammonia and others. They must be refined, to replenish exactly what is lost: oxygen, nitrogen and water. As the atmosphere is pushed away, also the greenhouse gasses will be lost into outer space. In case of Pluto in particular, there is another problem. Some gasses (oxygen, nitrogen) will be gas at low temperature, but when they are at higher elevations, they will be out from the reach of major greenhouse gasses. As so, a part of the runaway gasses will condensate and will snow down to the planet. What will that mean? When a snow of -180 C is flowing through the lower atmosphere, it will heat-up, cooling everything around. Pluto will require a huge amount of greenhouse gasses in order to increase temperature to a value acceptable for humans. This will trigger another problem. As gasses cool down, they create clouds. First, will be clouds of water ice. Far above them, clouds of oxygen and of nitrogen will get formed. In such conditions, there will be less light. This will make life for plants even harder, if artificial light is not introduced. In this example, we used Pluto, but if we consider another small celestial body, things will be more different. A smaller celestial body will tend to lose its atmosphere even faster. Solar winds will be an even bigger problem, but not for moons of Jupiter and Saturn (end even for moons of Uranus and Neptune), where strong magnetic fields can be of great help. On the other hand, Pluto has the advantage of a lack of external gravity. Triton, located close enough to Neptune, cannot develop such a fluffy atmosphere, because its upper gas layers will exit the Roche sphere (therefore, will get into Neptune's gravity field). Is it possible to use something heavier to compress the atmosphere of Pluto? An idea will be to use heavier gasses. Earth's atmosphere has nitrogen and oxygen, with some small amounts of noble gasses. Well, NASA found out that exactly the nitrogen is flying away from Pluto in stronger amounts. Xenon is the heaviest of all noble gasses (radon is the heaviest, but it's radioactive and has a short half-life). By replenishing nitrogen with xenon, we might get a heavier atmosphere. This will imply 3 major problems. First, xenon is rare. Finding and transporting so much xenon will be a hard job. Second, the heavy xenon will make other lighter gasses to separate. Stratification will occur. Much lighter oxygen will be pushed up and lost into space. Third, nitrogen is essential for life. without it, there will be no proteins. Will future settlers on Pluto agree to crash 4 comets every Earth year to replenish their atmosphere? Or will they prefer Paraterraforming instead? Update to update: Later, the New Horizons team concluded that Pluto is actually losing between 1/100 and 1/1000 less matter into space then previously estimated. Future reading: Atmosphere Parameters Category:Habitable Factors